1. Field of the Invention
The present invention relates to an image sensor unit used in an image reading apparatus, such as a copying machine, image scanner, facsimile and so on, and the image reading apparatus using the image sensor unit. In particular, the present invention relates to a paper sheet identification apparatus that authenticates a recording medium, such as a bill, security and so on.
2. Description of the Related Art
Well-known image reading apparatuses include a copying machine, image scanner, facsimile, paper sheet identification apparatus that authenticates a recording medium, such as a bill, security and so on. In such an image reading apparatus, a contact image sensor (CIS) unit that optically reads image information on an illuminated object and converts the information into electric signals is used. Patent Document 1 and Patent Document 2 disclose such a contact image sensor.
The contact image sensor unit is required to illuminates the object to be illuminated with a uniform illuminance at the reading position (along the reading line). For example, if an array of LEDs arranged at predetermined intervals in the main scan direction is used, such as in Patent Document 1 described above, the parts where the LEDs are arranged and the parts where the LEDS are not arranged can illuminate the object with difference illuminances. Thus, there is a problem that an illuminance unevenness occurs at the reading position for the illuminated object, and the image reading quality deteriorates.
To solve the problem, as with the image sensor disclosed in Patent Document 2, the illuminance at the reading position can be made uniform by increasing the optical path length from the LEDs to the reading position for the illuminated object, thereby diffusing the light from each LED. However, with the image sensor disclosed in Patent Document 2, the sensor substrate on which the sensor IC (light receiving element) is mounted that is disposed above the LED substrate on which the LED chip is mounted is disposed close to the light guide, so that the size of the sensor substrate has to be small. As a result, it can be difficult to mount a chip or the like other than the sensor IC on the sensor substrate. As a result, there is a problem that the sensor substrate needs to be connected, using a connector or the like, to another substrate on which the chip or the like other than the sensor IC is mounted, and the number of components increases.    Patent Document 1: Japanese Laid-open Patent Publication No. 2011-124741    Patent Document 2: Japanese Laid-open Patent Publication No. 2007-116590